U.S. Pat. No. 3,255,935 discloses a dispenser of the general type to which this invention relates. In the device of that patent, the piston is moved upwardly to force material out of the container, and for such motion the piston has a unidirectional driving connection with a rod that is in turn connected with a manually operable actuator. The unidirectional driving connection comprises a first set of four resilient tongues that have respective captive ends secured to the piston at its bottom. These tongues, which are arranged in diametrically opposite pairs, project obliquely downwardly from the piston and towards one another to have their free ends engaged under resilient bias against the rod. They thus constrain the piston to move in its upward discharge direction with the rod but permit the rod to slide downward relative to the piston. To confine the piston against downward displacement from any position to which it has been raised, four resilient tongues of a second set are attached to its bottom, likewise in diametrically opposite pairs, and these project obliquely downwardly and radially outwardly from the piston to have their free ends engaged under resilient bias against the inner surface of the cylindrical container wall.
This known dispenser has an actuator in the form of a push button that is accessible at its exterior and is connected with the upper end of the rod. When the push button is forced down, the rod moves downward with it, but the unidirectional driving connection comprising the first set of tongues allows the piston to remain stationary, restrained against downward motion by the tongues of the second set in their cooperation with the container wall.
This prior dispenser has the disadvantage that its tongues, which are formed integrally with a ring, must be produced very accurately with respect to both their dimensions and their biasing force, because otherwise easy actuation of the dispenser is not possible. If, for example, the tongues that engage the container wall exert too much spring force against it, the return spring in the push button will not be powerful enough to drive the piston in its discharge direction against the friction that those tongues produce by their engagement with the container wall. If, on the other hand, the length of those tongues is not held precisely, then there is a danger that when the rod moves downward it can draw the piston down with it, due to engagement of the rod against the surface of the hole in the piston through which it extends, and because the tongues of the second set, which are intended to engage the container wall, fail to bite into it owing to their excessive length. Corresponding problems are presented when the tongues of the first set are faulty with respect to their dimensions or spring forces.